Water Balance and Irrigation Performance Analysis at the Irrigation District level (Case study: Hamody irrigation system of khozestan)

Diagnosis of water management at the irrigation district level is required for therational modernization of the irrigation schemes and the subsequent increase in the efficiency of water allocation and application. The objective of this study is to evaluate globally in 3079 ha of land under modern irrigation system Hamody. The main district’s water inputs (irrigation، precipitation and canal releases) and outputs (actual evapotranspiration of crops، outflow surface drainage and canal seepage) were measured or estimated during the 1385 to 1388 hydrological years. The annual average water outputs were 16% higher than the corresponding water inputs، presumably due to canal seepage and lateral groundwater inflows from neighbor dry-land watershed. The district-level irrigation performance was poor (mean 1385-88 seasonal irrigation consumptive use coefficient- ICUC were equal 44%)، due to the low distribution (68%) and on-farm (53%) efficiencies for the 1385-88 irrigation seasons. Thus، despite the high volume of applied irrigation water، the actual district ET was 19% lower than the maximum achievable ET، indicating that the water-stressed crops yielded below their maximums. The evaluation by using neoclassical approach indicated that the values of net (0. 77) and effective efficiency (0. 65) were more than classical efficiency (0. 53)، in surface irrigation systems. The results obtained in this study showed that effective efficiency has suitable expression about irrigation management and method at farm scale، whereas net efficiency only considers concept of reuse of beneficial losses on spatial scale larger than the field. Potential reductions in water allocation were analyzed for three ICUC values (65، 75 and 85%) and two scenarios of modernization (I and II). In scenario I، where the aim was to achieve maximum ET and crop yields، water allocation could be reduced from 0 to 23% of the current allocation. In scenario II، where the aim was to achieve the maximum conservation of water under the actual ET and crop yields، reductions in water allocation would be much higher (from 31 to 47% of current allocation). Thus، significant volumes of water could be conserved in the rehabilitation of this district by increasing the distribution efficiency and، in particular، the onfarm irrigation efficiency.